A non-return valve having the features set forth in the definition of the species is known, for example, from the German Patent Application DE 44 39 880 A1.
Non-return valves are generally used for controlling the flow direction of a medium within a line, for example a pipe. The non-return valve automatically blocks the passage of the medium in a first flow direction and opens automatically in a second flow direction (referred to in the following and throughout the Application as the normal flow direction). Thus, if a higher pressure prevails at an inlet of the non-return valve than at an outlet of the non-return valve, the non-return valve is open, and a medium can flow from the inlet to the outlet thereof. If the pressure conditions are reversed, the non-return valve is closed by the higher pressure prevailing at the outlet. A bicycle tire valve or a valve on a motor-vehicle tire are simple examples of non-return valve applications.
To check lines or line systems having a plurality of lines, connections, valves, etc., for leaks, the line system to be tested, together with the valves, etc., is typically subject to the action of a test medium under pressure, and any resultant pressure drop is subsequently measured over a specific time interval. If the pressure drop is below a certain tolerance threshold, the assumption is that no leakage, etc. is present. If this not the case, other parts of the line system, etc., must be individually tested for leakage. If supplementary components, such as non-return valves, for example, are provided in the line system, they may, in some instances, prevent the test medium from being able to act on all parts of the line system, for instance when the test medium is introduced into the line system counter to the normal flow direction. Each of the non-return valves must then be bypassed by what is commonly known as a bypass line.
However, it is complicated, time-consuming and expensive to use these types of bypass lines, first of all, since the bypass line must itself be installed in each case and also activated when the line system is tested. At the same time, connections must also be provided for the bypass line, thereby additionally increasing the space requirements for the line system to be tested, since the placement of a bypass line must be considered when the line system is used.